Posts by keelan@mastodon.sdf.org
(DIR) Post #AYALtZ03r4D0shOL8C by keelan@mastodon.sdf.org
2023-07-28T17:44:56Z
0 likes, 0 repeats
And this is where things get interesting. The "adapter box" contains no active electronics. And even weirder, the RS-422 transmit/receive pairs pass through the box untouched. The ThunderScan doesn't connect to them at all. And the cable to the ThunderScan? Only 3 of the 4 wires are used. Subtracting two for power, that leaves only one wire. Somehow the ThunderScan connects to the mac through a single wire. And what is that wire is connected to? The serial port's handshake/ext clock pin. Whaaat?
(DIR) Post #AYALtbetyC497wVz4C by keelan@mastodon.sdf.org
2023-07-28T17:47:28Z
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Okay, so let's look at the "cartridge", that will answer all the mysteries. Maybe there is a microcontroller with some firmware we can dump to help decode the mystery. The front of the case near the sensor was glued shut, so after carefully prying it open, this is what I found:
(DIR) Post #AYALtfBGsIk03CgNRA by keelan@mastodon.sdf.org
2023-07-28T17:51:54Z
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It would appear that there are no digital electronics in this thing at all. Unsurprisingly, the part numbers were scrubbed from two critical components. The optical sensor, and a 10 pin TO-97 or TO-100 can. I happened to stumble across the optical sensor on Digikey (discontinued, obsolete), it's an HP HEDS-1500. When the ThunderScan was new, It was probably worth more than all of the rest of the hardware combined.
(DIR) Post #AYALti6Q0ndr71R2n2 by keelan@mastodon.sdf.org
2023-07-28T17:57:19Z
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That left the TO-100 package. Luckily it tuns out that very few products used that package. In fact I was only able to find one: an Analog Devices voltage to frequency converter. This is a handy device generates a square wave with a frequency that varies depending on a voltage input. And then it all started to make sense.
(DIR) Post #AYALtj3GU0iI3Wy2Vs by keelan@mastodon.sdf.org
2023-07-28T18:03:50Z
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So here's what's going on: the signal from the optical sensor goes through an op-amp, then it is fed into the V-to-F converter. The output from that converter is then fed directly into the clock in pin on the serial port. I'm assuming the software switches the SCC to async mode, and sends commands to the printer to start the carriage moving. Then it reconfigures the port into sync mode, disables interrupts and polls the "Rx Character Available" flag on the SCC...
(DIR) Post #AYALtkRlIPu2NnR7Kq by keelan@mastodon.sdf.org
2023-07-28T18:29:39Z
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It doesn't care about the data, it cares about timing. In my tests, the ThunderScan outputs a 2.6 KHz for black, 500 Hz for white. If the SCC were configured in sync mode with a synchronization character of all zeros, then that rate at which "characters" became available would vary depending on what the scanner was seeing. With 5 bit sync and data bits, black would generate a character every 3.8 ms, while white would produce a character every 20ms. Greys would be all the values in between.
(DIR) Post #AYALtlqc5VNMjA4Ti4 by keelan@mastodon.sdf.org
2023-07-28T18:35:10Z
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What's crazy about the ThunderScan is that it is a purely analog device. It is completely dumb, the moment the switch is set to "scan", it starts sending a square wave. The rest of the magic is done in software, which I'm hoping to get to next.That's it for now!
(DIR) Post #AZWMqr4lrdB2pLSYl6 by keelan@mastodon.sdf.org
2023-09-07T10:28:23Z
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@textfiles@mastodon.archive.org @textfiles@digipres.club are your retinas falling off?
(DIR) Post #AZWkANLuNoi3NWkj7g by keelan@mastodon.sdf.org
2023-09-07T14:37:17Z
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@textfiles@mastodon.archive.org @textfiles@digipres.club in retrospect this looks like a glib comment but I seriously was wondering if you were having an emergency retinal re-attachment procedure done because that’s what it sounds like!
(DIR) Post #Ab3rcFmEzcuxcl1f1s by keelan@mastodon.sdf.org
2023-10-23T09:12:10Z
1 likes, 1 repeats
@lpbkdotnet gave me a shoutout to @connections, but I realize I haven’t posted much telecom content recently! So here’s the exchange line circuit side of my British Ericsson 10+50 PABX, a version of the PABX 1 produced for export markets (in my case, Canada). Visible here are line relays for 50 extensions, the attendants circuit, the marker circuit, and 10 exchange line circuits. The other side of the cabinet contains the Strowger connectors.
(DIR) Post #AbB19uYeePjhM0Vxlg by keelan@mastodon.sdf.org
2023-10-26T18:23:33Z
5 likes, 5 repeats
Things in ascending order of bonkers:1. People move horses by plane2. People move enough horses often enough that there are dedicated horse transport flights. 3. There are enough dedicated horse transport flights that there are purpose built horse transport cargo planes with a small amount of passenger space for vets and horse people. 4. Theres a button that puts these planes into horse mode.
(DIR) Post #AbSY5MAFcOUMuuDSfA by keelan@mastodon.sdf.org
2023-11-04T02:36:10Z
2 likes, 3 repeats
What is this? This is a GPS receiver made by Trimble, one of the biggest GPS companies. Why is it shaped like an ambulance? Good question. This is a 6 channel GPS receiver from 1993, which was relatively early for consumer GPS tech. On the back is a Motorola 68HC000 and 64k of RAM. Look it even has a little red light on top. And a silk screened steering wheel.
(DIR) Post #AbTuvyDNmiN08W8Ncm by keelan@mastodon.sdf.org
2023-11-05T01:39:54Z
0 likes, 0 repeats
Everything else on store shelves is shrinking… but Haw Flakes appear to be growing? These things are enormous.
(DIR) Post #AcTR4XsHOMwVrSPIEy by keelan@mastodon.sdf.org
2023-12-04T17:45:22Z
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When I was a kid, half a kilometre from our house was a farm with a bunch of peacocks. My older brothers, being older brothers, had convinced me that the peacock's distinctive call was actually the sound of an injured mountain lion that was probably very aggressive and dangerous.
(DIR) Post #AcavMRzlF0JcAcJxAW by keelan@mastodon.sdf.org
2023-12-08T08:48:03Z
1 likes, 0 repeats
@duponin @mia for some reason this reminded me of this scenario that played out in a boring meeting once… Coworker: why are your laptops fans being so loud?Me: updates. Actually: grep -f /usr/share/dict/words /dev/urandom
(DIR) Post #AvGv5OZ79P8ZQxeg9w by keelan@mastodon.sdf.org
2025-06-19T00:47:06Z
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@vncresolver looks like oil separator tanks at an oil well
(DIR) Post #AvJ2SqFrSKavy0hGDo by keelan@mastodon.sdf.org
2025-06-20T01:19:03Z
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@foone I always thought it would suck if I had to reverse engineer something that used a bespoke virtual machine. Then I encountered a bespoke virtual and it was a lot of fun to take it all apart.
(DIR) Post #AwVXqlsHGffygNsIue by keelan@mastodon.sdf.org
2025-07-25T22:18:49Z
1 likes, 0 repeats
Annnnnnd now I'm admiring my Mom's meticulously crafted knitting machine patterns from 1991 in Ready, Set, Go! format.
(DIR) Post #Ay5U6ky1FACAB0opRQ by keelan@mastodon.sdf.org
2025-09-11T05:59:13Z
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@foone I can say for certain that it makes for a terrible autostereogram.
(DIR) Post #Aziz6SqiNAXeJ0KXOi by keelan@mastodon.sdf.org
2025-10-30T05:12:42Z
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@ricci I’m hosting all my stuff on a raspberry pi co-located in a small data center. The 5’s support for NVMe storage is a game changer. Best change I’ve ever made.